80 [July, 
ON SOME PECULIARITIES IN THE DEVELOPMENT OF HEMIPTERA- 
HETEROPTERA. 
BY J. W. DOUGLAS. 
(Continued from Vol. ii., p. 272, and Vol. Hi., 'p. 201 J 
2nd. — Abnormal structure of elytra and wings. 
The irregular development of the elytra among the Heteroptera 
is so common an occurrence that it could not fail to obtain the attention 
of writers on the Semiptera. By some of them the apterous examples 
of Velia currens were deemed to be a species distinct from the winged 
ones. By others the examples of various species that are apterous or 
have rudimentary elytra have been considered as larvse or pupae 
endowed with procreative powers ; and Curtis even supposed that such 
imperfectly developed organs indicated a state of existence analogous 
to that of the pseudimago of the JEphemeridce, although no pellicle, as 
in that case, was ever known to be cast off by apterous Semiptera. 
All these theories are inconsistent with the facts that individuals 
destitute of elytra and wings never attain these organs ; that in others 
the proportion of development of the elytra in any case attained is 
final ; and that, in all instances, the insects are in all other respects 
perfect and adult, and perform every function of their existence. It is 
true that in apterous or semi-apterous forms the thorax (especially 
the pronotum) is less robust and often differs in outline, the reason 
being doubtless the smaller size of the alary muscles ; but this in no 
way interferes with the course of the insect's life. 
The cause of this irregular development is obscure. Some authors 
have thought that great heat has an influence in perfecting the alary 
organs, and some of the instances adduced seem to favour this hypothesis. 
On the other hand, some species are apterous in all climates ; in some 
the ? is always semi-apterous ; and in those species where perfectly 
winged individuals rarely occur they are found at the same time and 
place as those imperfectly developed, all being of the same brood, and 
subject to the same climatic influences. I remember at this moment 
that several winged examples of Velia ctirrens, a state at all times 
scarce, were captured in the peculiarly cold and wet autumn of 1866, 
one of them in Scotland. Rather, I think, should we consider the 
development or non-development of the organs of flight to be due to 
the elasticity of constitution (so to speak) inherent in species, whereby, 
under certain circumstances, some individuals assume the most perfect 
condition of which their species is capable, and so are enabled to fly 
away to keep up the vigour of the race by pairing with mates of a 
different brood, while the remainder are left to the chances and changes 
